1. Field of the Invention
This invention relates to a method and apparatus for manufacturing air bearing sliders for use in computer storage devices, and more particularly to a method and apparatus for forming edge contours on such air bearing sliders.
2. Description of Related Art
Magnetic recording systems utilizing transducers that are supported by an air bearing layer as they move relative to the surface of a magnetic recording disk are well known in the art. Each transducer is mounted in a slider assembly which has a contoured surface. The air bearing is produced by pressurization of the air as it flows between the disk and slider, and is a consequence of the slider contour and relative motion of the two surfaces. The purpose of the air bearing is to provide a very narrow clearance, with minimal or no contact, between the slider and rotating disk. Thus, transducers "fly" on a layer of pressurized air at just a few microinches above a rotating disk surface. This allows a high density of magnetic data to be transferred and reduces wear and damage to the magnetic assembly and recording media during operation.
Typical sliders of the prior art, as illustrated in FIG. 1, utilize at least two lower rails 1a, 1b having flat surfaces 2 oriented toward the recording medium and extending from the body 5 of the slider. Each of these rails 1a, 1b has a tapered forward surface 3a, 3b oriented against the direction of rotation 4 of the recording medium. The rotating recording medium forces air by viscous effects into the tapered forward surfaces 3a , 3b, and thereby produces a pressure beneath each of the rails 1a, 1b, resulting in the air bearing. These sliders are typically gimbal-mounted to a load beam assembly which is attached to an arm. The arm is driven by an actuator which positions the transducer over the recording surface from one data track to another. The arm can move in a linear motion (which is termed linear access) or it can rotate about a pivot point (which is termed rotary access). With rotary access, the slider will be positioned at varying angles with respect to the direction of the disk rotation as the slider moves over the recording surface. This angular orientation is referred to as the "skew" angle.
When a typical slider is positioned so as to have any angular skew, the rotation of the recording medium introduces pressurized air at the forward edge of the slider, thereby generating the air bearing. However, this air is pressurized at a reduced value because of the skew, thus giving rise to a reduction in the flying height. Also, the skew angle gives rise to a roll of the slider such that the air bearing flying height is not uniform under both of the rails 1a, 1b. Accordingly, the position of the transducer with respect to the recording medium can vary as the slider is caused to roll in one direction or the other or fly at different heights. Such variations in flying height adversely affect the data transfer between transducer and recording medium. In particular, the density of bit storage is adversely affected if the flying height of a slider is increased.
Furthermore, the slider must move radially across the recording medium at a substantial rate of speed to access various portions of the medium. This motion also introduces air under one edge of each slider rail 1a, 1b and results in a roll of the slider and a change in the spacing between the transducer and the recording medium. When any of these variations of spacing occur, particularly with a substantially reduced spacing between the slider and the recording medium, contact may occur between the slider (and its transducer) and the recording medium, or at least potentially rough surfaces thereof. Any such contact causes wear to the slider and the recording surface.
Moreover, the relative speed between the magnetic disk and the slider varies as a slider moves from an inner diameter of the recording medium to an outer diameter. Such variations in speed result in variations of air flow under a slider, which changes the flying height of the slider. As noted previously, such variations in flying height adversely affect the data transfer between transducer and recording medium.
One solution that has been proposed for minimizing change in the flying height and roll of a slider as skew angle or relative air flow speed changes is to provide a transverse pressurization contour along each side edge of the air bearing surfaces 2 of the slider, such that any air flow from the side of the slider assembly due to skew angle and/or access velocity produces pressurization adjacent to one side edge and depressurization (or expansion) adjacent to the other side edge of each air bearing surface 2. Selection of transverse pressurization contours (or "TPC"s) can be made which makes the slider assembly flying height and roll angle essentially insensitive to skew angle and/or access velocity and/or air flow speed. A design of a slider having such a transverse pressurization contour is disclosed in U.S. Pat. No. 4,673,996 ("the '996 patent"). The '996 patent shows three transverse pressure contours for air bearing sliders (see FIGS. 6 and 7 of the '996 patent). However, a problem arises with such TPC designs in fabricating the fairly precise angles or angular structures required to form the transverse pressurization contour on an air bearing edge. Considering the contours shown in the '966 patent, the angled contours of the left hand air bearing surface of FIG. 6, and the rounded contours shown in FIG. 7, are difficult to manufacture on a repetitive, reliable basis.
The step structure of FIG. 6 of the '966 patent is generally preferred over other transverse pressurization contours. However, such a structure is quite expensive to manufacture. Normally, such a step structure could not be machined into the slider air bearing surface using conventional machining. The depth of the step is typically about 30 microinches, .+-.5 microinches. Conventional machining in a production environment permits tolerances of only about .+-.300 microinches.
One method of fabricating such step structures is to etch (e.g., chemically etching) the slider material. However, most sliders are made of calcium titanate or polycrystalline ferrite material, zirconia, or alumina titanium carbide (for thin film heads). These materials are not generally etchable with the degree of precision required to make a step structure. While single-crystal ferrite material can be chemically etched, this material is, at present, quite expensive, and requires a relatively expensive photomasking operation to shield portions that are not to be etched. Another method for forming TPC step structures is ion milling. However, this process is also expensive.
In accordance with another method for fabricating TPCs on a slider, taught in U.S. Pat. No. 5,156,704, assigned to the assignee of the present application, slots are formed in a slider blank adjacent the location where air bearing surfaces are to be formed. The slots are filled with an etchable material (e.g., glass), and the slider blank is then machined to form air bearing structures. The etchable material is then carefully etched to form TPC step structures. However, this method requires a number of steps to be performed, and still involves substantial costs.
Independently, while working to improve the wear of the slider and the disk, it was discovered that blending the edge of air bearings to improve the wear of the slider and the disk affected the flying height, since the blends are TPCs. However, it was determined that some such techniques adversely affect the flying height characteristics of the slider. For example, a common method for blending a slider, referred to as "spin blending", is illustrated in FIG. 2a. In the method of FIG. 2a a slider 200 is rotated about a central axis 201. A sheet of flexible tape 203 coated with an abrasive substance is stretched across the slider 200. Stretching the tape 203 across the air bearing surface of the slider 200 causes greater pressure to be applied to the outer edges 205 of the rails of the slider 200. As the slider 200 rotates, the edges 205 are abraded to conform to the general contour of the curvature of the abrasive surface around the edges 205.
This method of abrading the edges of a slider by generating a relative motion between the slider and an abrasive tape is relatively inexpensive and can be relatively well controlled. However, spin blending adversely affects the flight of a slider. Spin blending primarily affects the outer edges 205 of the slider rails. This results in undesirable rolling and changes in the flying height as the slider changes radial distance and skew angle when rotary actuators are used to position the slider with respect to a disk, as is common practice today.
In response to the undesirable flying profile which resulted from spin blending, a variation on the process, referred to as an "X-Y blending technique" was developed. FIG. 2b illustrates the X-Y blending technique. A slider 200 is mounted within a window 208 of a fixture 210. The window 208 generally conforms to the outside dimensions of the slider 200 to capture the slider 200. The fixture 210, and hence the slider 200, moves in two orthogonal directions X, Y which define a plane parallel to the air bearing surfaces of the slider 200. The slider 200 is placed in contact with a lapping film 212 which has a soft, compressible backing. A force F is applied by the fixture 210 to the slider 200 to press the slider into the lapping film 212. The relative X-Y motion of the slider 200 with respect to the lapping film 212 causes the edges 214 of the slider to be abraded. Due to compression of the backing of the lapping film, both edges 214 of the rails of the slider 200 are abraded without abrading the air bearing surfaces. X-Y blending is capable of providing a more symmetrical blend, and thus improves the flying profile across the disk of a blended slider. This method of blending the edges of a slider by generating a relative motion in two orthogonal directions between the slider and an abrasive surface on a compressible backing is also relatively inexpensive and can be relatively well controlled.
However, the X-Y blending technique has the disadvantage that the inside edges are not blended as deeply as the outer edges. Also, the relative amount of contouring at each outside edge is essentially the same, and the contouring at each inside edge is essentially the same as each other inside edge, but may be different from each outside edge contour. In some cases, it is desirable for the contour at the inside edge of a first rail and the outside edge of a second rail to be equal, and the contour at the inside edge of the second rail and the outside edge of the first rail to be equal but different from the first contour.
Therefore, it would be desirable to form, with high precision, non-uniform contours on the air bearing edges of a slider rail. Such non-uniform contours may be formed in any combination of blends, such that the best combination of edge contours may be formed to provide as close to uniform flying height as possible, and to allow greater control over the amount of lift provided by the air bearing at various points on the air bearing surface of the slider. The present invention provides a method and apparatus for achieving these objects.